The Short Message Service (SMS) is a popular means of communication over mobile networks in which subscribers can send data, predominantly, text messages across the mobile network to other subscribers. Different mobile technology domains have been introduced over recent years and it is now possible to send SMS messages over IP Multimedia Subsystem (IMS), Packet Switched (PS) and Circuit Switched (CS) domains. Often the devices of mobile subscribers will be registered on multiple technology access domains simultaneously.
In the network architecture for SMS delivery, when a sending party sends a Short Message (SM) to a target party, the sending party's home network provides the SM to either the home network or serving network of the target party and waits for confirmation that the SM has been delivered successfully. In the former case, the home network of the target party takes responsibility for delivering the message and also takes responsibility for retrying in the case of a delivery failure. In the latter case it is the sending party's home network that takes responsibility. However, this case limits the mobile technology access domains to which the SM can be delivered to PS and CS.
After the sending party network has forwarded the SM to the respective target party network and before it receives confirmation that the message has been delivered, the sending party's home network keeps open the communication channel (or “dialogue”) with the target party's serving network. This open dialogue takes up network resource and, in busy and congested networks, it is inefficient to keep this dialogue open for any extended time period. This problem is exacerbated in the case where the home network of the target party takes responsibility for delivering the SM, as it has to try potentially up to three mobile technology access domains for delivering the SM to the subscriber (i.e. IMS, PS and CS). The case where the sending party's home network takes responsibility for delivering the message is less problematic as the sending party's home network will receive a response after trying each mobile technology access domain and so can better manage its network resource.
Current networks only keep the communication dialogue open for a predefined time period after the SM has been forwarded to the target party's network. This is managed by a delivery timer. Typically, this time period is between one and ten minutes. Network operators regularly set the timer to one minute in order to release their network resource as soon as possible. If the sending network receives confirmation that the message has been successfully received by the receiving party before the expiry of the predefined time period the timer is stopped and the resource is reallocated. However, if no confirmation is received before the expiry of the predefined time period, the delivery timer times out. Upon time out, the sending network may either: a) immediately try to send the message again by resending the message request to the target party's network (possibly with the same failed outcome); b) initiate a procedure to receive an identifier from the receiving party's network when the target party's device (UE) becomes available; or, c) give up entirely and assume there is some system failure in the target party network.
None of these outcomes are entirely satisfactory. In cases (a) and (b) above, the recipient may end up receiving the SM twice, or, the resending of the SM may produce an error in the target party's network, which is currently trying to deliver the first message. In case (c) the recipient may not receive the SM at all.
In the case that the target party is registered in multiple mobile technology access domains, the sending party's home network or the receiving party's home network (depending upon which has taken responsibility for delivering the message) will page each technology access domain in turn until it finds the technology access domain upon which the UE is currently residing (if it is the sending party's home network though, only two mobile technology access domains can be attempted). Typically, both the sending party's home network and the target party's home network will use a predefined mobile technology access domain hierarchy for paging the target party's UE. Once the SM has been delivered successfully, the target party's serving network confirms to either the sending party's home network or target party's home network that the SM has been delivered successfully, and the communication dialogue is closed (and resources can be reallocated to other purposes).
As more mobile technology domains are introduced and utilised by networks and subscribers, the chances of delivery taking longer than the predefined time out period is increased since the networks may have to try several technologies before finding the one on which the device is currently camped.
One solution would be to increase the time-out period of the sending party's delivery system. However, this would increase the maximum period for which the sending party resource was taken up. Therefore, this is not an ideal solution.
The applicants have appreciated that errors can occur when the delivery timer of an SM times out before the home network of the sending party or the target party has successfully delivered the SM. It is not an ideal solution to extend the period of the delivery timer.